1. Field of the Invention
The present invention relates to a network relay apparatus and a method of combining packets in a network in which, as in the Internet Protocol (IP), packet size is variable in length and maximum transmission unit (MTU) size for the network is predetermined primarily according to the physical medium and communication standard, and in which communications are performed by the network relay apparatus (router) controlling transmission paths.
2. Description of the Related Art
A network relay apparatus in a network in which packet length is variable as in the Internet Protocol (IP) performs transmission path control (routing control) according to the packet destination by using routing information gathered and stored in advance. In the network relay apparatus, even when a plurality of packets addressed to the same destination network have arrived in a bursty manner, the routing control is performed on a packet-by-packet basis.
In such prior art, even when a plurality of packets addressed to the same destination network have arrived at the network relay apparatus in a bursty manner, the routing control has had to be performed on a packet-by-packet basis, and this has been a factor working to increase the processing load of the network relay apparatus.
To solve this problem, Japanese Unexamined Patent Publication No. 1-241243 proposes a method that reduces the routing control processing load of the network relay apparatus by combining a plurality of packets and thereby reducing the number of packets.
In a network, a value called the maximum transmission unit (MTU) is set for each physical medium. This value specifies the maximum packet size (the number of octets) that can be transmitted over the physical medium. If the MTU of the physical medium on the route along which a packet is transmitted is smaller than the size of the packet, the network relay apparatus either discards the packet or fragments it to the MPU size for transmission.
More specifically, in the method of Japanese Unexamined Patent Publication No. 1-241243, when combining packets, no account is taken of the MTU of the medium or the network to which the combined packet is transmitted; accordingly, even when the number of packets is reduced by combining a plurality of packets for transmission, if the MPU of the transmission path is smaller than the combined packet size, the packet transmitted is discarded or fragmented, resulting in an inability to make full use of the effect achieved by combining packets.